I like good 'ole, PURE, Simple Green right out of the bottle. The stuff works great for degreasing. They made a bicycle cleaning foam that works great too. It will clean chains, cassettes and other nasty things very quicky. Wet area to be cleaned, spray on foam, let sit 1 minute, wash with warm soap and water. Ti bike frames look GREAT after this process. 
WD-40 is great to break down rust, not too good of a lube.
WD-40 is great to break down rust, not too good of a lube.